A natural, nontoxic product called genistein-combined polysaccharide, or GCP, which is commercially available in health food stores, could help lengthen the life expectancy of certain patients with prostate cancer. The most likely to benefit are men with prostate cancer that has metastasized and who have had their testosterone lowered with drug therapy.

Lowering of testosterone, also known as androgen-deprivation therapy, has long been the standard of care for patients with metastatic prostate cancer, but life expectancies vary widely for those who undergo this treatment. Testosterone is an androgen, the generic term for any compound that stimulates or controls development and maintenance of male characteristics by binding to androgen receptors. A current study's findings hold promise for GCP therapy as a way to extend life expectancy of patients with low response to androgen-deprivation therapy.

The research focused on GCP, a proprietary extract cultured from soybeans and shiitake mushrooms and marketed by Amino-Up of Sapporo, Japan. Researchers found that the combination of the compounds genistein and daidzein, both present in GCP, helps block a key mechanism used by prostate cancer cells to survive in the face of testosterone deprivation.

The research team, led by Paramita Ghosh, PhD, of UC Davis School of Medicine, had earlier shown that when a patient's androgen level goes down, cancerous prostate cells kick out a protein known as filamin A, which is otherwise attached to the androgen receptor in the cell's nucleus. The androgen receptor regulates growth of prostate cancer cells. Once filamin A leaves the cancerous cell's nucleus, that cell no longer requires androgens to survive. Thus, loss of filamin A allows these cells to survive androgen deprivation, and the cancer essentially becomes incurable.

This study shows that GCP keeps filamin A in the nucleus. As long as this protein remains attached to the androgen receptor, the cancerous cells need androgens to survive and grow. They die off when starved of androgens, thus prolonging the effects of androgen deprivation, which ultimately prolongs the patient's life. This study was published in Endocrine-Related Cancer (2012; doi:10.1530/ERC-12-0171).

The team's hypothesis is that patients with metastatic prostate cancer who have the weakest response to androgen-deprivation therapy could be given GCP concurrently with androgen deprivation therapy to retain filamin A in the nucleus, thereby allowing cancer cells to die off.

The researchers are now pursuing funding to begin GCP human clinical trials. Because GCP is a natural product rather than a drug, and requires fewer government approvals, these trials are expected to proceed rapidly once funded.

“We should know within the first eight months or so of human clinical trials if GCP works to reduce PSA levels,” said Ralph de Vere White, also of UC Davis. “We want to see up to 75% of metastatic prostate cancer patients lower their PSA levels, and GCP holds promise of accomplishing this goal. If that happens, it would probably be a greater therapy than any drug today.”